Means to operate electrostatic telephones



July 10, 1928. 1,676,452

s. LOEWE Isms TO OPERATE ELECTROSTATIC TE'JEPRONES Filed April 29, 192'? INVENTOR SIEGMUND LDEWE BY 0. MM Ma AT ORNEY lliapi i ia insane T101? OF AIVIB'RICA, A CORPORATION OF DELLAl/V ARE.

MEANS TO OPERATE ELECTROSTATIC TELEPHONESi Application filecliipri129, 1927, Serial No; 187,678,- and in Germany February 0,: 192-4:

Telephones and loud speakers operating on basis ofthe electrostatic principles, for many reasons, are fundamentally suited for the reproduction of signals and in wireless telephony work than the devices working according to the electromagnet c principles, for they involve neither hysteresis nor ohinic losses nor saturation phenomena, all of which are inevitable in electromagnetic processes. The denieritof electrostatic telephones and loud speakers resides in that the In the first place, the requisite high constant biasing potential, according to the iiivention, is not obtained by 111621113013 batteries or cells, but rather by rectified radio frequency currents. It is possible in this ianner to provide the required biasing potentials even in values oliseveral thousand volts in a way free from danger and with:

a minimum amount of equipment.

,From the method of producinghigh-biasing potentials as here disclosed there may be derived further a. number of novel circuit arrangements for reception work, and these shall also be described hereinafter, and theyconstitute part of the present invention.

In the accoinnan in drawing: Fi ure 1' L H D c 2') shows acircuit arrangement heretofore used including an electrostatic telephone wherein the high potentials required are obtained by the use of batteries or accumulators,

Figure 2 shows a circuitarrangement including'an electrostatic telephone the high potentials for which are supplied according to my inventionzan'd Figure 3 shows an improved receiving circuit utilizing an electrostatic telephone.

Figure 1 illustrates a receiving arrangeinent comprising an electrostatic receiver telephone of the kind heretofore customarily used, in'dia rraininatic representation. Under practical conditions, a plurality of ain-' plifier stages is used, it being; understood that the requisite number of amplifier stages must be imagined as inserted in the circuits at the proper place. 7 J

Referring to Figure 1,1 denotes the receivingrantenna, 2 is a secondary circuit, 3 an grid condenser, 1 a leak resistance, 5 an audion tube comprising filament 6, grid 7, and plate 8. 9' is the-"heating"battery, 10 the plate battery, 11 ahigh resistance, 12. the high-potentialbattery, 18' the static receiving telephone or the loud speaker:

The tube '5, can be seen, is operated in an audion circuit arrangement.- The poten tial fall across resistance 11 varying. accordinn to the inconiingcurrents is: added" to the 1 potential of'battery 12 andresu-lts in corresponding acoustic actions in. the loud speaker 13.

Now, according to this invention, the high potential 12 is produced in as. wayias showir in F inure 2L Instead'of the battery 12, 2, condenser 14L is provided whose capacitance is high coinparedrwith the capacitance of the telephone; Connected with the said condenser l l -is a rectifier tube 15in series with a coil 16 which, in turn, is coupled with a circuit 17 which is excited with" high fre" quency energy froinra tube 18', forinstance, in a voltage-dividerscheine. The'higli-po tential arising: at the condenser 14- is entirely undangerous since, in case of accidental contact therewith, such an important potential dropis occasioned-at once that no danger can any longer. Between condenser 18 and. the potential source 14 a choke coil may further be inserted.

As l'GfHI'dS the electrostatic telephone 13'," Y

the his n potential thus produced actsin the very same way as a biasing potential' de rived from batteries,

its to the rest, the receivingactions are thesaine as shown in 'Figure- 15 However, it has to be noted that" themethod of deriving a variable potential across the terinina-lsof a-resistance ll'; which is inserted; invthe plate: circuit" of an audiorrtube, is very unsatisfactory, since" theeam resistance 11, because of its necessary high value, renders the platepotential 10 largely ineffective in so far as the tube isconcerne'd. On the other hand, any attempt of changing the variations of the plate current into highpotential variations by the aid of transformers is impossible of practical realization seeing that the transformers required therefor would have to beprovided with a very high number of primary turns because of the low strength of the primary current flowing in the plate circuit, so that a still higher number of secondary spires would be needed to the end of insuring an increase in potential. Transformers of this type are not only extremely expensive, but they also are of very low efficiency since the rise lIl potential is largely lost again by virtue of the internal capacity of the transformer.

However, the problem of transferring the modulated incoming currents to the electrostatic telephone in an efiicient manner is easily solvable rather perfectly by that receiver circuit a "rangcments are used which produce amplified, but also modulated receiving oscillations in the plate circuit of a tube, the frequency of these oscillations, as will be noted, not having to be the same as that of the incoming oscillations.

One embodiment of the scheme is shown by way of example in Figure 8. v

The audion receiver arrangement is brought by way of a resistance 11 which is connected withv the grid 19 of a tube 20 connected in a self-excitation scheme. plate circuit 21 of this tube is as free from damping as possible and works with a small condenser and a large coil so that high potential amplitudes are obtained. Regeneration is produced by means of a coil 22 which is connected in series with a stopper condenser 23, a parallel resistance 24 being further provided, if desired. 25 is the plate battery of tube 20, 18 is the loud speaker, and 14 the condenser, to which, as shown in Figure 2, means for producing high potential is arranged in parallel. It willbe noted, however, that coil 16 in this case may also be coupled directly with coil 21 so that another tube 18 and a further oscillation circuit 17 may be dispensed with.

Now, the arrangement operates in the following way: Tube 20 would produce continuous waves of considerable amplitude, if the latter were not considerably diminished by the condenser 23 or even entirely suppressed. This results in a negative charging of grid 19 whereby the plate current is choked. The (normal) current of tube 5 occasions a drop of potential. across resistance 11 whereby also a negative po tential is produced at the grid 19. However, as soon as currents come in, oscillations are produced in circuit 21, the potential amplitude of which may be a multiple of in which local oscillations are released at The l the rhythm of 'the incoming signals, for instance, arrangements in which tube 5 itself is connected in parallel relation to con denser 23 so that resistance 11 could then be dispensed with, operate in a similar way as the circuit arrangement last described.

I claim as my invention:

1. Radio signalling apparatus comprising a vacuum tube having plate and grid circuits regeneratively coupled together, means in series with the grid circuit for suppressing oscillations due to the regenerative coupling, an electrostatic telephone and a condenser in series, across a portion of the plate circuit of the tube, means for supplying a rectified high frequency current across said condenser, and means for coupling the output of another tube in said radio signailing apparatus across the grid and filament of said first mentioned vacuum tube.

2. Radio signalling apparatus comprising a vacuum tube having plate and grid circuits regeneratively coupled together, means comprising a condenser and a resistance in series with the grid circuit for suppressing oscillations due to the regenerative coupling,

an electrostatic telephone and a condenser in series, across a portion of the plate circuit of the tube, means for supplying a rectified high frequency current across said last mentioned condenser, and means for coupling the output of another tube in said radio signalling apparatus across the grid and filament of said first mentioned vacuum tube.

3. Radio receiving apparatus comprising an input circuit connected across the gridand filament of a first vacuum tube, means for coupling the output of said first vacuum tube to a second vacuum tube, a tuned circuit in series with the plate of said second tube and inductively coupled to an inductor in series with the grid of that tube, a circuit comprising a resistance and a capacity in series with said inductor, an electrostatic telephone and a condenser in series, across the tuned plate circuit, and means across said last mentioned condenser for supplying a rectified high frequency current thereto.

SIEGMUND LOEVVE. 

